1. Field of the Invention
This invention relates to a solid state imaging device, such as a CMOS sensor and CCD, and a method for manufacturing the same, and a solid state imaging module.
2. Background Art
Solid state imaging devices, such as a CCD (charge coupled device) and CMOS (complementary metal oxide semiconductor) sensor, are widely used in cameras, mobile phones, and personal computers. Demand for downsizing of solid state imaging devices is increasing year by year. To this end, there have been a number of innovations, and various configurations have been proposed.
In a known structure including a solid state imaging device, an imaging device substrate provided with the solid state imaging device is placed on a circuit substrate including an external circuit, and electrodes on the imaging device substrate are connected to electrodes on the circuit substrate by wire bonding. This structure has a problem in downsizing because of the large area of the bonding region.
In response, a structure is proposed as a technique for downsizing. In this structure, a window is provided in the circuit substrate, an imaging device substrate is placed thereon so that the imaging device section is aligned with the window, and the electrodes of the imaging device substrate are connected to the electrodes of the circuit substrate by flip chip mounting (JP-A-2001-128072). This structure has the problem of light being incident on the imaging device from its backside because the backside of the imaging device substrate is exposed. To solve this problem, there is proposed a technique of providing a light shielding layer illustratively made of metal evaporated film or black resin entirely on the backside of the imaging device substrate (JP-A-2001-128072).
Recently, as a structure for further downsizing the solid state imaging device, a structure having a backside electrode has been proposed. In this structure, the imaging device substrate is provided with a penetrating electrode, for example, by which the frontside of the imaging device substrate with an imaging device formed thereon is electrically connected to the backside opposed thereto, and the interconnect of the imaging device is routed from the frontside to the backside. The imaging device substrate is placed on the circuit substrate, and a solder ball on the backside electrode of the imaging device substrate is connected to the electrode on the circuit substrate by flip chip mounting. This structure is highly expected to realize further downsizing as compared with the structure disclosed in JP-A-2001-128072. In this backside electrode structure, the circuit substrate is placed on the backside of the imaging device substrate. Hence, basically, light is not incident from the backside of the imaging device substrate. Thus, no case has been reported on the problem of backside light incidence in solid state imaging devices of the backside electrode structure.
However, according to the inventor's study, it has turned out that the problem of backside light incidence occurs also in the backside electrode structure. More specifically, in this structure, the circuit substrate is placed on the backside of the imaging device substrate. However, a solder ball having a height of several ten micrometers is interposed between these substrates, which are not in close contact with each other. Hence, light enters this small gap from the substrate periphery and reaches the backside of the imaging device section of the imaging device substrate. This causes a serious problem in the case where the imaging device is highly sensitive.
Furthermore, the height of the solder ball varies with variation in the conditions for its manufacturing process. It has thus turned out that the amount of light incident on the backside of the imaging device substrate greatly depends on the variation in the manufacturing process. Hence, this problem of backside light incidence greatly affects the yield of solid state imaging devices, and thus greatly influences the cost.
On the other hand, with regard to a solid state imaging device of the backside electrode structure, there is proposed a technique for forming a reflecting layer or antireflective film between the imaging device and the backside electrode to prevent light incident on the imaging device substrate from the frontside from being reflected at the backside and being incident on the imaging device (JP-A 2007-189198 (Kokai)).